Network systems for the transmission of data between a plurality of nodes or terminals are of increasing interest in the data processing field. For example, optical systems utilizing fibre optic transmission with various network configurations, employing either active or passive couplers and dividers with both wavelength and time division multiplexing, are being developed at the present time. Uses include broadband overlay for subscriber access networks and ultra-high capacity packet switching for telecommunication or parallel processing computer applications. See for example A. Oliphant "Progress in the development of a digital optical routing system for television studio centres", International Broadcasting Convention IBC 88, Brighton, Sep. 88, IEE Conference Publication No. 293 pp 90-94, D. B. Payne & J. R. Stern "Single mode optical local networks", Conf. Proc. Globecom '83, Houston, paper 39.5 and E. Authurs et al "A fast optical cross connect for parallel processing computers" Proc. 13th European Conference on Optical Communication, Helsinki, Finland, Sep. 1987.
Such systems offer capacities which are orders of magnitude greater than electronic (time multiplexed) networks, complete flexibility of interconnect configuration, service transparency and considerable facility for future upgrades.
In order to make a particular connection between the nodes of such a network the optical receiver in the receiving node must be tuned into the same wavelength as the required transmitter. The switching and reconfiguration of connections in the network can be achieved either by switching the wavelength of transmission with fixed separate wavelength receivers at each node or by using fixed separate wavelength transmitters in each node and switched wavelength receiver.
For high speed reconfiguration of the interconnection pattern such as required by telecoms or computer packet switching applications it is necessary to devise a very rapid communication protocol between the nodes for setting up the required interconnection pattern. This is very much easier to achieve using wavelength switched transmitters and fixed wavelength receivers because in this case the network becomes "self routing" with messages automatically directed by the transmitter to the correct receiver. A good example of such a network is shortly to be published by E. Authurs et al. "HIPASS : an optoelectronic hybrid packet switching system" IEEE Jnl. on selected areas of Communications Dec. 1988. A disadvantage with this type of network is that it requires wavelength switched transmitter components which are very difficult to fabricate with adequate performance. A further disadvantage of conventional networks is the difficulty of providing a broadcast facility in which one node can broadcast a message to all the other nodes. This can introduce severe problems in maintaining the correct time sequence of signals.
The object of the present invention is to minimize or to overcome these disadvantages.
Reference is directed to our co-pending U.S. application Ser. No. 07/432,574 which relates to a multi-wavelength optical network comprising a plurality of nodes interconnected via a single common passive optical coupler wherein all signals transmitted over the network are synchronous at the coupler, each node receiving signals from all the nodes and each node including wavelength demultiplexing means.